繊維状3CaO・Al_2O_3・3CaCO_3・32H_2Oの合成と性質

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As one of the serial studies on fibrous calcium compounds, the synthesis of fibrous C_3A・3CaCO_3・32H_2O was studied by adding CaCl_2 solution (6-21×10^<-3> mol dm^<-3>) to the solution prepared by introducing CO_2 gas or by adding Na_2CO_3 solution (CO_3^<2->concentration : 1-5×10^<-3> mol dm^<-3>) into NaAlO_2 solution (7-22×10^<-3> mol dm^<-3>). Characteristics of the product obtained by liquid-phase reaction in CaCl_2-NaAlO_2-CO_2 and CaCl_2-NaAlO_2-Na_2CO_3 systems were determined by means of X-ray diffraction, thermal analysis (TG-DTA), scanning electron microscopy, infrared spectroscopy and chemical analysis. The formation of fibrous C_3A・3CaCO_3・32H_2O was affected remarkably by synthetic conditions such as pH, initial Ca/Al atomic ratio and concentration of CO_3^<2->ion. When the concentration of CO_3^<2->was 1-3×10^<-3>mol dm^<-3>, the initial Ca/Al atomic ratio to form fibrous crystals of C_3A・3CaCO_3・32H_2O was less than 0.3 in CaCl_2-NaAlO_2-CO_2 system and less than 2.0 in CaCl_2-NaAlO_2-Na_2CO_3 system. Thus, the fibrous crystals were stable at pH above 11.7. Therefore, when the initial Ca/Al atomic ratio exceeds 0.3 in the system of CaCl_2-NaAlO_2-CO_2, pH because less than 11.7, yielding no fibrous crystals. While, the reaction in CaCl_2-NaAlO_2-Na_2CO_3 system to form the fibrous crystals progressed successfully because the pH value was kept over 11.7 even in the initial Ca/Al atomic ratio 0.3-2.0. It was confirmed that fibrous C_3A・3CaCO_3・32H_2O crystallized as high crystalline fibers with aspect ratios above 300 elongated parallel to c-axis in hexagonal through an unstable amorphous phase which was precipitated in the initial step. The fibrous shape was stable in heating up to 300℃. Furthermore, the packing state of the fibrous crystals as filler for paper was discussed.
社団法人日本セラミックス協会の論文
1992-08-01

繊維状3CaO・Al_2O_3・3CaCO_3・32H_2Oの合成と性質

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